Switch controlling means



p 1933- G. H. WHITTINGHAM 1,927,479

SWITCH CONTROLLING MEANS Filed Feb. 8, 1932 Patented Sept. 19, 1933UNITED STATES PATENT OFFICE SWITCH CONTROLLING MEANS ApplicationFebruary 8, 1932.

2 Claims.

This invention relates to improvements in electromagnetic switches orcontactors, adapted for use on alternating current circuits. Contactorsare generally designed to suit a voltage in the supply wires which iskept constant except when trouble arises on the power line or at thecentral station which may cause temporary lowering of the voltage orcomplete failure of current. As long as the voltage is normal, the usualform of contactor will operate satisfactorily; but if, while thecontactor is closed, the voltage dies away on the line to the pointwhere the switch starts to open, introducing a gap in the magneticcircuit, the reactance of the magnet coil will be lessened and thecurrent flowing through the coil will be increased, causing attractionof the armature toward the magnet, with a resulting decrease in currentin the coil, and these back and forth fluttering movements of the switcharm will cause burning and perhaps welding of the contacts, if longcontinued. Again, if current fails in the supply circuit while thecontactor is closed, the switch arm will fall to open position and ifthe current returns to the wires with gradually increasing voltage, theswitch arm will approach the closed position before the voltage on thesupply circuit becomes normal and will flutter and burn the contacts. Insuch case, if the subnormal voltage is long continued, the coil of thecontactor magnet may be injured by the excess current which it takes,and apparatus, such as induction motors, on the work circuit which thecontactor connects to the supply circuit may become overheated andburned out.

By means of the present invention, in case the voltage drops to apredetermined point, the contactor will open without fluttering of theswitch arm or burning of the contacts, and if the current on the linefails and then returns, the switch '40 will not close until the voltageof the supply circuit is practically normal, thus preventing injury tothe switch contacts and magnet coil and to motors, etc. on the workcircuit. In the accompanying drawing, The figure is a diagrammatic viewillustrating the preferred form of the invention, and,

Referring to the drawing, L and L indicate supply wires leading from analternating current source, and a indicates a contactor adapted tocomplete a circuit from the supply wires to a load such as lamps or anelectric motor. The contactor comprises an armature 1 hinged to one endof a U-shaped core 2 of a magnet b and adapted to form a closed magneticcircuit through the core when the con- Serial No. 591,701

tactor closes and the armature engages the opposite end or" the core.One side of the load circuit extends from conductor L through conductor3 to stationary contact 4, thence through the contactor arm to conductor5. The other side of the load circuit is indicated at 6, extending fromthe supply wire L.

The circuit for the coil of the magnet 12 extends from conductor 6through a switch 7, resistance 8 and conductor 9 to the coil 10 of arelay 0, thence by conductor 11 to the coil 12 of the contactor magnet,thence by conductors 13 and 3 to the side L of the supply circuit. Theresistance, relay coil and. the magnet coil of the contactor will thusbe normally connected in series. The function of the relay is to close ashunt around the resistance. One terminal of the resistance is connectedby conductor 14 to relay contact 15 and the other terminal of theresistance is connected by conductor 16 to contact 17. As shown, 7 therelay comprises an iron core 18, within the coil 10, suspended by aspring 19 from an adjustable supporting screw 20. A metal bridge piece21 is arranged on the relay core below the contacts 15 and 17. When thecoil 10 is energized 0' sufficiently, the core lifts and the part 21bridges the contacts, thereby short-circuiting the resistance; and whenthe core drops, the resistance is again placed in series with the coilof the relay and contactor magnet. The amount of resistance 5 in serieswith the coils may be adjusted as desired by means of a contact arm 22connected to the shunt conductor 14 and adjustable along the resistance,

The operation of the invention as illustrated in the drawing is asfollows: Assuming the line voltage to be normal, when the switch '7 isclosed current will flow in series through the resistance 8 and coils 10and 12. The current value will be below that required for causing thecontactor magnet to actuate its armature but it will be suflicient tocause the relay to lift its core and bridge the contacts 15 and 17,thereby shunting the resistance 8. A greater current flow willimmediately follow in the coil 12 and the magnet b will attract thearmature l, and the armature will close the magnetic circuit through thecore 2. This will instantly increase the reactance of the magnet coil 12and the current flowing through this coil and the relay coil will bereduced to such an extent that the relay core will immediately drop andopen the shunt around the resistance 8. Thereafter, as long as the linevoltage is normal and the switch '7 remains closed, the resistance 8will remain in series with the coil of the contactor magnet. It will beseen that the resistance is in series with the coil of the contactormagnet at the start; that it is momentarily cut out to increase thecurrent flow through magnet coil of the contactor so that the magnetwill have sufficient strength to close the switch arm, and theresistance is then again inserted in series with the magnet coil,reducing the current flowing through the coil while the switch isclosed.

If, now, while the contactor is closed, the voltage on the supply wiresis reduced, from any cause, to the point where the magnet will releaseits armature, the switch arm will drop back to its open position withoutfluttering and burning of the contacts, because the resistance in serieswith the magnet coil will prevent the heavy surges of current in themagnet coil which would result from opening the magnetic circuit iftheresistance were not present. After the contactor has opened, byreason of lowered voltage, the switch cannot close until the voltageagain builds up to practically normal voltage, and during all the timethat the voltage is subnormal, the resistance will prevent the magnetcoil from receiving excessive current. As the voltage returns to normal,and when within a volt or two of normal, the relay will operate tobridge the resistance and the magnet coil will receive the heavy currentrequired to cause the magnet to close the switch. Immediatelvthereafter, the reactance of the magnet coil will so reduce the currentflowing in the relay coil that the relay will be de-energized and openthe shunt around the resistance, leaving the latter in series with themagnet coil.

What I claim is:

1. The combination with an alternating current supply circuit, anormally open switch, a magnet for closing said switch and a circuit forthe coil of the magnet connected to the supply circuit, of a. resistancein series with said coil sufficient to prevent the magnet from closingthe switch while the voltage in the supply circuit is below apredetermined value, and a relay having a coil connected to the supplycircuit in series with the coil of said magnet, said relay adapted tocut out the resistance when the voltage approximates said value. topermit the magnet to close the switch, and to re-insert the resistancewhen the switch has closed.

2. The combination with an alternating current supply circuit, anormally open switch, a magnet for closing said switch, and a circuitfor the coil of the magnet connected to the supply circuit, of aresistance in series with said coil suflicient to prevent the magnetfrom closing the switch while the voltage in the supply circuit is belowa predetermined value and a relay having a coil connected to the supplycircuit in series with said magnet coil and with said resistance, saidrelay adapted to cut out the resistance when the voltage approximatessaid value, to permit the magnet to close the switch, and to re-insertthe resistance when the switch is closed.

GEORGE H. WHITTINGHAM.

